1. Field of the Invention
The present invention relates to a workpiece transfer apparatus of an independent type which rationally performs the loading of an unfinished workpiece onto and the unloading of a finished workpiece from each of a plurality of machine tools performing the same machining function.
2. Description of the Prior Art
In a prior workpiece transfer apparatus of the aforementioned type, as shown in FIG. 1, there are disposed in parallel loading and unloading conveyors C1 and C2, along which a plurality (e.g. two) of machine tools M1 and M2 performing the same machining function are disposed, and further, a pair of manipulator carriers 1 and 2 are guided for travelling along an over-head transfer rail 3 extended between a machining station of each of the machine tools M1, M2 and the loading and unloading converyors C1, C2. However, such construction of the transfer apparatus leaves a problem to be solved in that a plurality of workpieces each awaiting a successive machining operation are stocked in that portion of the loading conveyor C1 which extends between the machine tools, thus increasing the number of undesirable in-line stock workpieces. Such construction of the transfer apparatus, moreover, makes it difficult for an operator to monitor the machining operation that each machine tool is performing, since except by turning around the corner of either of the machine tools as indicated by the broken line, he is not able to come from the front of one of the machine tools to the front of the other machine tool, and vice versa. Further, the conveyors C1 and C2 provide obstacles on the passing way of the operator. Although bridges crossing over the conveyors C1 and C2 are installed in places, the provision of the bridges does not bring about a perfect solution in obviating such restraint on the operator's passing.
Another prior transfer apparatus has also been known, wherein as shown in FIG. 2, a pair of machine tools performing the same machining function are disposed respectively at both sides of serially arranged loading and unloading conveyors C1 and C2, and wherein a pair of manipulator carriers 1 and 2 are guided for travelling along an overhead transfer rail 3 extended transversely of the conveyors C1, C2. In this transfer apparatus, workpieces that are stocked on the loading conveyor C1 for machining on either of the machine tools are advantageously decreased in number. However, the conveyors obstruct the way of an operator from one of the machine tools to the other machine tool, and this disadvantageously makes it difficult for the operator to monitor machining operations of both of the machine tools as well as to quickly approach the same.